Containers having metal walls and/or a jacket and bottom, particularly decorated aerosol cans, are embodied either by one piece or several pieces. In the case of one-piece aerosol cans made of aluminum, the cylindrical can body is produced with cold extrusion. Subsequently, a valve seat is formed at the open end by way of compressive necking down. This type of production process is very expensive due to the installation required for the many treatment steps as well as the water and energy requirements for cleaning and drying. The references U.S. Pat. No. 4,095,544 and EP 0 666 124 A1 describe the production of seamless steel cans, wherein a cylindrical can body is manufactured from a steel sheet coated with tin or plastic material by punching, pressing and ironing. It has turned out that enormous problems occur with forming restricted neck portions, because the structure of the material is changed and/or hardened by the ironing.
Also widely used are cans made from sheet steel for which the jacket has a longitudinal welding seam. The bottom and the upper closure are attached to the can jacket by folded seam connections. With folded seam connections sealing problems can occur which, for example, are reduced with the aid of sealing rings. With standard cans having extremely thin walls, problems occur with seals that are arranged on the end faces. To dispense with the sealing rings and to reduce the high material requirement for folded seams, it is proposed in WO 02/42196 to attach the lid of a filled beverage can by way of laser welding to the can jacket. For this, the upper edge of the jacket and the outer edge of the lid with identically aligned end faces are placed against each other, are welded together along the end faces, and rolled over to avoid sharp edged.
It is also possible to roll over only the outer edge of the lid or the jacket, so that the lid and/or the jacket fit on the outside and on the inside against the jacket and/or lid and the end face of one part is encircled by the reshaped edge of the other part. The finished connection therefore always has at least three material layers that fit against each other, thereby resulting in a high material use and appearance of the folding seam, which is undesirable for many uses.
References EP 200 098 A2 and EP 208 564 disclose additional embodiments of two-part and multi-part cans, for which a bottom or an upper closing part is attached by way of laser welding to the can jacket. The above-described laser welding seams between can wall and bottom and/or end piece do not permit a cost-effective production with sufficiently high piece numbers per time unit and/or result in unattractively formed connecting regions. With embodiments where the end faces of the can jacket and the closing part both are aligned and point toward the outside, sharp edges are created that interfere and must be folded or rolled over, thereby undesirably increasing the material consumption and, for many applications, creating an undesirable appearance of the folding seam.
Embodiments according to the EP 200 098 A2, for which a cylindrical bottom region must be joined by pushing together or overlapping to the cylindrical end region of the can material, could be produced only with sufficient material thicknesses and extremely high production and feeding precision. With extremely thin can material, a gap-free joining of the cylindrical regions and/or their end faces, which fit one into the other or which are joined to each other, is hardly possible because even small deviations in the circumference prevent a precise joining. If the two end regions, particularly the end faces, do not fit precisely against each other along a short partial section of the circumference, it is not possible to create a tight laser welded seam.
The device described in the EP 200 098 A2, where an expanding body is arranged inside the cylindrical can jacket, cannot correct the gaps in the circumference of the seam to be created and the associated areas where air can enter. During the expanding, the can material is reshaped by way of at least two mold parts that can be moved toward the outside, so as to assume a shape that corresponds to the outside edge of the form parts. In circumferential direction, spaces exist between the form parts in which the can jacket is not supported. This supporting surface, which is interrupted in circumferential direction, cannot safely ensure an air-free contact between the thin-walled cylindrical regions to be welded together. Closed seam lines between cylindrical joining regions for cans made from thin sheet steel therefore cannot be created precisely and such that they are sealed, or at least not with little expenditure and at high speeds.
In addition, the welded seam is not sealed on the can inside, so that corrosion cannot be ruled out, thereby restricting the can to the use of non-corrosive content. A further disadvantage is that a welding seam at the cylindrical can jacket harms the appearance of the can and/or requires a decoration to be subsequently affixed to the cylindrical outside can surface to cover the welded seam.
The known longitudinal welding seams, particularly the laser welded seams known from the EP 208 564 and U.S. Pat. No. 4,341,943, are provided with offsets and/or thickness differences in circumferential direction, which lead to problems when creating a neck portion or during the insertion of a bottom and/or an upper closing part. With these offsets, a tight seal and/or a tight connection to a closing part can be achieved only with difficulty. The offsets are also not desirable for aesthetic reasons and can lead to problems if the cans still need to be coated with a film. When welding together overlapping joining areas, the danger exists that the overlapping area and thus the circumference vary slightly. Expensive holding devices with end stops must be used directly at the welded seam for a precise overlapping, which can result in problems. With thin sheet metals coated with an anti-corrosion plastic coating on the inside, the coating is easily damaged through the welding operation and the corrosion protection is no longer ensured.
For aesthetic reasons and to mark the contents, a decoration is applied to the outside of the jacket surface. Imprinted films are affixed to the can body according to known solutions, so as to dispense with an expensive and inflexible direct imprinting of the can body. According to the EP 0 525 729, a decorative film is wrapped in peripheral direction directly around the can body and is joined to form a closed film enveloping the can body.
Removing a section of film and affixing it to the can body is very difficult with thin films and/or is connected to problems. Solutions are known from references U.S. Pat. No. 4,199,851, DE 197 16 079 and EP 1 153 837 A1 where a shrinkable flat plastic material is wound around a mandrel to form a closed sleeve, which is then pushed in axial direction as all-around label onto bottles or cans to be shrunk on. Pushing the all-around label over the bottles and/or cans carries the danger of deformation and damage, particularly with thin films. Besides the operational and frictional forces, friction-caused electrostatic charges and connected, variable electrostatic forces that act upon the film can occur, so that a fast transfer of the cylindrical, closed film is extremely problematic.
The known solutions for producing cans involve expensive installations. The cans therefore cannot be produced at the filling plants, which results in high transportation costs for transporting the empty cans from the can manufacturer to the filling plants. The known methods of forming can bodies with laser-welded seams are not suitable for can bodies that can be formed in many different ways from thin flat material and/or which comprise a large share of material in the joining regions, which projects toward the outside. According to prior art, the edge regions of thin can material cannot be joined with acceptable expenditure and air-free along the seam line.